Production manner null of circular billet for martensite type stainless steel seamless steel tubes production

摘要

PURPOSE:To obtain a round billet capable of perfectly avoiding the occurrence of internal surface defects at the time of piercing-rolling by forming the structure in the central part of an ingot of the stainless steel with a specific composition into a rolled structure by means of primary rolling and then reducing the amount of precipitation of delta-ferrite by means of soaking and holding at specific temp. CONSTITUTION:An ingot of a martensitic stainless steel having a composition containing, by weight, 0.12-0.30% C and 11-14% Cr is heated and subjected to primary rolling by means of ordinary blooming, etc., by which the cast structure in the central part is changed into rolled structure. The primary rolled stock is soaked and held again in a soaking furnace at a temp. of the delta-ferrite precipitation temp. on the equilibrium diagram of this steel or below and then finished into a round billet of the prescribed outside diameter by means of ordinary billeting. By using the above round billet as stock and carrying out piercing rolling on an inclined rolling system represented by Mannesmann piercer, the rate of the occurrence of internal surface defects at the time of piercing rolling can be reduced.